We have studied the effects of thrombin on porcine aortic tropoelastin and find that it gives discrete cleavage in approximately seven or eight parts of the molecule, producing large peptide fragments which are amenable to sequence studies. We have isolated two of these fragments and partially sequenced them. We are in the process of isolating the remaining six fragments and plan, during the coming year, to begin primary structural studies on these, using classical degradation techniques. BIBLIOGRAPHIC REFERENCES: L. B. Sandberg, E. Bruenger, and E. G. Cleary, "Tropoelastin Purification: Improvements using Enzyme Inhibitors" Analytical Biochemistry, 64, 249-254 (1975). B. L. Rasmussen, E. Bruenger, and L. B. Sandberg, "A New Method for Purification of Mature Elastin," Analytical Biochemistry, 64, 255-259 (1975).